Transverse Zeeman background correction for graphite furnace laser excited atomic fluorescence spectrometry: determination of lead and cobalt in standard reference materials

Abstract

Transverse Zeeman background correction was applied, for the first time, to Laser Excited Atomic Fluorescence in an Electrothermal Atomizer (ETA-LEAFS), and compared to Longitudinal Zeeman background corrected ETA-LEAFS. The system used for this work was a modified Perkin-Elmer Zeeman/5100 furnace/magnet assembly, designed to give a higher magnetic field than the standard commercial unit. Zeeman sigma component energy level splittings were determined for both lead and cobalt by measurement of the atomic fluorescence spectral profile, with magnetic “field on”, as a function of laser wavelength. The splittings were 0.0055 nm and 0.0060 nm for lead and cobalt, respectively. The detection limits for lead and cobalt were 4 and 500 fg, respectively, which were within a factor of two of those without background correction. The shape of the calibration curve, and the linear dynamic range of six to seven orders of magnitude, were not affected by Zeeman background correction. The precision for Zeeman ETA-LEAFS (ZETA-LEAFS) was determined to be 5% for aqueous solutions. Lead and cobalt were determined in National Institute of Standards and Technology (NIST) standard reference materials. Lead was accurately determined in slurried samples of estuarine sediment, coal fly ash and citrus leaves by simple aqueous calibration, with precisions in the 6–14% range. Cobalt was determined in coal fly ash and estuarine sediment by the use of dissolved sampling, and palladium matrix modification, with sample precisions of 5–7%. Cobalt could not be determined accurately by use of slurried samples due to sample matrix interferences. Transverse Zeeman background correction was shown to correct for ETA black body radiation, and backgrounds caused by the addition of 20 μg of AlCl 3 to cobalt aqueous standards.